1. Technical Field
The invention relates to dispensing devices and more particularly to a motionless mixer tube for mounting on the end of a dispensing device for mixing together at least two liquid materials, such as resin compounds. More particularly, the invention relates to such a motionless mixer tube for mixing and dispensing small volumes or shots of the mixed material.
2. Background Information
An increasing number of products require the dispensing of liquid or semi-liquid flowable materials in one form or another for their manufacture. These flowable materials typically comprise two chemically reactive component resins. The types of materials dispensed include various flowable liquid, semi-liquid or pastes such as epoxies, polyurethanes, silicones, polyesters, acrylics, polysulfides, as examples. Common commercial manufacturing processes in which such materials are used include injecting precise amounts of mixed resins into molds, encapsulating electric components with insulating resins, applying continuous beads of structural adhesives, injecting sealing joints and numerous other functions requiring the accurate control, delivery and mixing of two reactive component materials. Examples of the product application which use small volumes of the mixed resins include under the hood electronic assemblies and safety devices for the automotive and trucking industry, encapsulation of magnetic and electrical devices, such as the mounting of components on circuit board assemblies for switches, power supplies, heating assemblies and other electronic components for various industries.
Thus, as the aforesaid flowable mixed materials continue to be consumed in increasing quantities the demand for precise liquid and semi-liquid metering, mixing and dispensing devices and equipment is also growing at an accelerated rate. The industry is continuously searching for more reliable, efficient and accurate dispensing devices for plural component flowable materials for a variety of purposes. For example, a particular application may require that a device efficiently and accurately mixes and dispenses such plural materials ranging in shot or dot sizes from 0.00003 cubic centimeters to several cubic centimeters.
When dispensing such small volumes of such plural mixed components, it is extremely harmful for even very small air bubbles to be trapped within the dispensing nozzle since they are difficult to purge and will materially affect the amount of resin being dispensed and the mixing thereof. The purging of such air bubbles is more easily accomplished in dispensing devices, and in dispensing tubes and nozzles for larger discharged shots or streams of material than set forth above. However, the air bubbles that are trapped occasionally can become larger than the actual size of the shot of material to be dispensed from the nozzle when small volumes or shots are being dispensed, and thus present a very serious problem and are difficult to satisfactorily purge from the equipment.
Some examples of prior art metering, mixing and dispensing devices for two component liquid materials are shown in U.S. Pat. Nos. 5,092,492; 4,095,722 and in pending patent application Ser. No. 08/115,820 filed Sep. 3, 1993, and assigned to the same assignee as is the present application. When the two component resins are dispensed from a liquid metering and dispensing device, such as shown in U.S. Pat. No. 5,092,492 and the above identified pending application, the two components are dispensed into a motionless mixer, preferably of the type which has a helical mixing element therein, wherein the two separate streams are completely and thoroughly mixed and combined as they move through the mixing element before they are discharged from the outlet end of the motionless mixer. Again, it is the prevention of the formation of air bubbles in these motionless mixers, especially when used for dispensing extremely small volumes of mixed components that must be eliminated.
Furthermore, it is desirable that these motionless mixers, which for many applications are inexpensive, disposable, throw-away items, be able to be securely attached and removed quickly and conveniently from the discharge end of the dispensing equipment, and that when used for extremely small shots, that the dispensing needle thereof be easily attached and removed from the end of the motionless mixer for cleaning, repair, replacement, etc.
Therefore, the need exists for an improved motionless mixer tube for use with liquid metering and dispensing devices in which plural component materials are metered and dispensed from the device into the motionless mixer for subsequent mixing and dispensing at the point of application. Moreover, the need also exists for such a motionless mixer tube which is easily attached to and removed from the metering device, and which permits the easy, rapid and secure attachment of a dispensing needle on the discharge end of the motionless mixer tube, and that the motionless mixer tube prevents or greatly reduces the formation of air bubbles therein.